High blood pressure can occur in pregnancy in two forms. It may be a preexisting condition, called chronic hypertension, or it can develop during pregnancy--a condition known as gestational hypertension. It is also called toxemia or preeclampsia and occurs most often in young women with a first pregnancy.
AC relays. AC relays are manufactured similar to their DC counterparts. If AC current is applied to a DC relay, the relay will pulse at the frequency of the AC current. To overcome this problem, the core is equipped with a shading ring on one-half of the core (Photo 2).
Typically the relay will operate a switch (relay contact) to indicate that an input has surpassed a setting, or the relay can provide notification through visual feedback such as a meter or LED. One advantage of electronic or microprocessor relays is an ability to communicate with a network or a PLC. As an example, a thermostat can be evaluated using the diagram in Figure 1. The input that is measured is temperature and the protection relay input device is the temperature sensor. The user sets the desired temperature setting (pick-up level). The relay measures the existing air temperature and compares it to the setting.